The present invention relates to a cardio-respiratory recording system and, in particular, to a portable, multi-channel polygraph system for recording and replaying ECG, respiratory effort, respiratory airflow, and oxygen saturation levels in order to document abnormal sleep respiration patterns, most notably apnea.
Traditionally, polysomnography studies have been conducted using either two-channel pneumocardiograms (i.e. ECG and respiratory impedance data) or multi-channel recordings of sixteen to twenty channels. Although performed more conveniently, two-channel recordings are limited in the amount of information they can provide for meaningful diagnosis. Sixteen to twenty channel studies, in contrast, are limited to sleep laboratories with corresponding higher study costs associated with the capital equipment, personnel and plant. A trade-off must thus normally be made by the clinician or diagnostician between limited data, which can produce misdiagnosis or missed significant respiratory events, and almost unlimited data with its greater attendant costs.
Of the systems of which Applicant is aware, sensor data is collected from two to twenty channels relative to a separate time channel, or through calibration of mechanical components of a system which may vary in speed and could effect timing and rate calculations. Data is typically collected and displayed one channel per track without multi-plexing or overlaying physiologically distinguishable data on a single track during replay. For example, heart rate data is either displayed as a singular trace heart rate line at relatively slow chart rates or as individual QRS waveforms at a fast chart rate. Both are not shown together on a single track. Applicant is also not aware of any system particularly displaying heart rate data with a hash or "tic" mark relative to the trend or trace line to indicate the time occurrence of each QRS complex.
Similarly and relative to O2 saturation and motion artifact, applicant is unaware of any system which distinguishes motion from true O2 desaturations. Additionally existing systems do not provide periodic calibration levels as reference points. Such multiplexed data, not only maximizes the data display, but also provides meaningful information to the clinician to permit on going confirmation of the oximetry sensor calibration which may change over the course of a study session.
A need therefore exists for an economical data collection system of fewer than 12 to 20 channels in a portable construction whereby a subject's sleep patterns may be monitored at home or in a clinical setting and which data may be used in evaluating and pre-screening suspected sleep or other cardio-pulmonary disorders. Advantages are thereby attainable to the clinician and third-party payors. In the case of infants and out-patient care, apnea monitoring programs may also be more economically conducted on a longterm basis.